Many applications require the measurement of pressure at a remote location, but some of these applications are more difficult to implement due to atmospheric conditions where the measurement is made. For example, pressure measurements are needed in sewers to control and manage water and sewage flow, but the environment in the sewer is moist and damaging to electronics, as well as potentially explosive. Although the pressure measuring electronics can be placed inside a housing, in order to measure pressure relative to atmospheric pressure, it has been necessary to include a vent to atmosphere to permit detection of atmospheric pressure in order to make the measurement, which means that moisture from the surrounding atmosphere can enter the housing and damage the electronics, as well as posing a threat of ignition of explosive gasses in the environment.
In the prior art, electronics for a pressure sensor have been positioned within a housing, and a vent tube has been pneumatically connected from the pressure sensor to the housing, to carry atmospheric pressure to the pressure transducer so that measured pressures may be referenced to atmospheric pressure. In this approach, to control moisture, a desiccant has typically been installed at the housing end of the pressure transducer's vent tube, to absorb moisture and prevent moisture from entering the vent tube. While this solution addresses the infiltration of moisture, it requires regular replacement of the desiccant when its moisture absorbing capacity is diminished. Furthermore, because the vent tube carries pressure from inside the housing to the sensor, if the housing is sealed, the housing pressure, not atmospheric pressure, is delivered to the sensor, causing inaccuracy. If, however, the housing is unsealed to allow its internal pressure to equalize with atmosphere, the venting exposes electronics and electrical connections in the housing to outside atmosphere, which can present problems to the electronics in an environment containing moisture, and more severe problems when the environment contains other more corrosive gasses. Furthermore, if flammable gasses can infiltrate the housing the electronics can pose a risk of igniting those gasses.
In other prior art, a pressure transducers for sensing external air pressure have been mounted in a bellows or bladder inside of a generally unsealed electrical control housing. While this solution isolates the pressure transducer from moisture, it does not prevent the infiltration of moisture to other electronic components, nor does it address the problems inherent with atmospheric exposure of electronics and electrical connections in potentially explosive or corrosive environments.